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  • The radius of curvature of the curved surface of a Plano-convex lens is 20 cm. If the refractive index of the material of the lens be 1.5, it will A. act as a convex lens only for the objects that lie on its curved side.

The radius of curvature of the curved surface of a Plano-convex lens is 20 cm. If the refractive index of the material of the lens be 1.5, it will

A. acts as a convex lens only for the objects that lie on its curved side.
B. acts as a concave lens for the objects that lie on its curved side.
C. acts as a convex lens irrespective of the side on which the object lies.
D. acts as a concave lens irrespective of the side on which the object lies.

Answers (1)

 The correct answer is option (c).

Explanation:-

Act as a convex lens irrespective of the side on which the object lies. The relation between f,\mu ,R_{1} and R_{2} is known as lens maker's formula and it is

\frac{1}{f}=\left ( \mu -1 \right )\left ( \frac{1}{R_{1}}-\frac{1}{R_{2}} \right )

R_{1}=\infty ,R_{2}=-R

f=\frac{R}{\left ( \mu -1 \right )}          

Here, R=20 cm, \mu =1.5. On substituting the values, we get

f=\frac{R}{\mu -1}=\frac{20}{15-1}=40\; cm

As f>0 means converging nature. Therefore, the lens acts as a convex lens irrespective of the side on which the object lies.

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infoexpert23

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